Projection display devices are in increasing demand because they allow large-screen display to be realized relatively easily, with minimal device size and at low cost compared to direct-view display devices. Projection display devices having projectors that employ liquid crystal display elements as two-dimensional optical switch elements differ from projection display devices employing CRT projection tubes, in that they use a dot matrix display allowing reproduction of images displayed to high precision without blurring up to the peripheral sections of the screen. This technology therefore offers the most potential for high-definition digital televisions.
Their images are projected onto a screen. The screens are largely of two types, namely reflective screens that are observed from the projector side and transmissive screens that are observed from the side opposite the projector with the screen in the middle.
Transmissive screens are normally composed of a fresnel lens sheet and a lenticular lens sheet. A lenticular lens has rectilinearly shaped lenses situated in a regular pattern, and therefore images are prone to the moire effect.
Japanese Unexamined Patent Publication HEI No. 2-77736 discloses a transmissive screen have a construction wherein spherical lenses are spread over a transparent base and the lenses are fixed with a transparent resin. A screen having this construction does not require a die for manufacture and hence no limits are placed on its size during manufacture. Consequently, it is possible to realize a large-picture transmissive screen without seams. In addition, incident light from the spherical lens side is condensed by the lens effect and isotropically scattered, thereby producing a wide-angle display both horizontally and vertically. However, glare often occurs depending on the angle, and may reduce the display quality.
Transparent screens that are attached to show windows and produce images of moving or still advertisements are also known. Such transparent screens ordinarily employ hologram elements, whereby projected light from a projector provided on the opposite side of the viewer from the hologram element is projected onto the hologram element to form an image, and the hologram element diffracts and scatters the projected light forward allowing the viewer to recognize an image. (Japanese Unexamined Patent Publication HEI No. 11-202417)
However, hologram elements are extremely expensive, while they are limited in their diffraction and scattering angles and thus have restricted viewing angles. Furthermore, because hologram elements require strict placing of the projector, screen and viewer, they offer very little freedom of installation.
On the other hand, it has been attempted to provide reflective screens with improved contrast by selective reflection of only certain specific polarized light.
For example, Japanese Unexamined Patent Publication HEI No. 5-107660 and Japanese Unexamined Patent Publication No. 2005-17751 disclose circular polarized reflective screens employing cholesteric liquid crystals. These exhibit enhanced contrast by reflecting specific circular polarized light and absorbing the opposite circular polarized light. The invention described in Japanese Unexamined Patent Publication No. 2005-17751 controls the reflective properties to reduce glare caused by mirror reflection.
Japanese Patent Public Inspection No. 2002-540445 discloses a reflective screen of a type which reflects specific linear polarized light by a multilayer structure. This screen has a mirror surface that causes glare, and therefore it has not been developed. Also, International Patent Publication No. WO03/098346 describes an invention whereby the aforementioned reflecting polarizing plate and scattering polarizing plate are combined to reduce glare.